The following discussion of the background to the invention is intended to facilitate an understanding of the invention. However, it should be appreciated that the discussion is not an acknowledgement or admission that any of the material referred to was published, known or part of the common general knowledge as at the priority date of the application.
In many existing buildings, particularly older buildings, the plumbing of the building has been used for electrical earthing purposes. That is, the plumbing has been used to earth fittings of the building because the plumbing generally has an extensive and continuous path through the building that extends to earth and that is relatively accessible for earthing purposes. Moreover, in older buildings, the plumbing conduit or tubing is often copper which is electrically conductive. In these forms of plumbing installations, the tube couplings which are used to connect tubes or fittings together must also be electrically conductive so as not to disturb the earthing circuit. To achieve this, the tube coupling must include an internal conductive path which provides electrical continuity between the parts of the tube coupling that engage the tubes or fittings and between the housing of the tube coupling which typically will be brass and which typically forms a bridge between tubes and/or fittings for electrical flow.
Prior art tube couplings that provide electrical continuity exist. For example, British patent GB 2,380,532 provides an arrangement in which the circumferential edge of the grab ring of the tube coupling is formed to include one or more projections that are forced into engagement with the inside surface of the tube housing when a tube is inserted into the tube coupling. While this arrangement provides acceptable electrical contact between the grab ring and the housing, the projections as formed on the circumferential edge of the grab ring are not easy to produce because they are so small and these grab rings are either not used where electrical contact is not required or are used with a non-conductive cartridge ring. As such, the one form of grab ring is not universally appropriate for all forms of tube coupling.
Alternative arrangements have included a conductive cartridge ring, which is interposed between a metallic grab ring and the housing of the tube coupling, and which is made of machined brass. The grab ring is in contact with the cartridge ring at all times and the cartridge ring is in contact with the housing at all times so that upon contact between the grab ring and the outside of a tube that is inserted into the coupling, electrical continuity is ensured from the grab ring to the housing.
One problem with the above form of prior art, is that the use of brass for the cartridge ring adds expense to the cost of the tube coupling, not only because brass is more expensive than other metals, but also because a cartridge ring in brass requires the cartridge ring to be machined, which is an expensive form of manufacture. Another problem is that the tolerance between components of coupling must be close to ensure that contact between the grab ring, the cartridge and the housing is always maintained.
The present invention seeks to provide an alternative arrangement which provides one or more benefits over the prior art discussed above.